I measure the pH of samples from my effluent system and I have noticed a black deposit forming on the diaphragm of my electrode. What causes this deposit and what can I do to remove it

This deposit is formed by the reaction between sulphide ions in the effluent with silver ions from the electrode’s reference system, forming silver sulphide – an insoluble compound.

If left unchecked, the silver sulphide deposit will eventually clog the electrode’s diaphragm, reducing its accuracy and response time until eventually no meaningful readings can be taken.

The silver sulphide can be removed using Reagecon’s Inorganic Electrode Cleaning Solution (Product IECS5). The electrode should be regularly cleaned with this cleaning solution as part of a preventative maintenance program.

Further details on the care and maintenance of pH electrodes are given in the Reagecon Technical Paper “Care, Maintenance and Fault Diagnosis for pH Electrodes”